It is generally considered desirable to reduce the level of noise within a vehicle passenger compartment. External noises, such as road noise, engine noise, vibrations, etc., as well as noises emanating from within passenger compartments, may be attenuated through the use of various acoustical materials. Accordingly, sound attenuating materials for vehicles, such as automobiles, are conventionally used in the dashboard, in conjunction with carpeting for floor panels, in the wheel wells, in the trunk compartment, under the hood, and as part of the headliner.
The attenuation of external noise is conventionally referred to as sound transmission loss (STL). The attenuation of internal noise is conventionally referred to as sound absorption. The acoustic impedance of a material is defined as material density times acoustic velocity, and is expressed in units of Rayls (Newton-seconds/meter3). Acoustic impedance defines how easy it is for air to move through a material. Thus, for fibrous materials, acoustic impedance depends upon the density of the fibrous material and fiber diameter. Generally, the heavier the blanket and the finer the fibers, the higher the acoustic impedance. Moreover, thicker layers typically have more acoustic impedance than thin layers. The ability of a material to attenuate noise is conventionally defined by the material's STL, acoustic impedance, and absorption characteristics.
Carpeting used to cover the floor areas of vehicles, such as automobiles, is conventionally molded into a non-planar three dimensional contoured configuration which conforms to the contours of the vehicle floor so as to fit properly. In order to make the carpeting moldable and shape-sustaining, it is conventionally provided with a backing of thermoplastic polymer composition. The thermoplastic polymer backing also serves as a barrier to improve the sound deadening properties of the carpet assembly.
Dash insulators are often mounted to a vehicle firewall which separates the passenger compartment from an engine compartment. Dash insulators are designed to reduce the transmission of noise and heat from the engine compartment into the passenger compartment. Conventional dash insulators consist of an acoustical absorber such as an open-cell polyurethane foam or a resinated fiber pad which faces the fire wall, and a barrier sheet such as a heavily filled thermoplastic material. Dash insulator barriers are conventionally produced in a compounding process followed by an extrusion or calendaring process or by an injection molding process to achieve a barrier sheet of desired thickness and width.
FIG. 1 illustrates a conventional dash insulator 10 for reducing noise and heat transmitted from an engine compartment of a motor vehicle 12 into a passenger compartment. The dash insulator 10 is adapted to be mounted inside the passenger compartment of the vehicle against substantially the width of a fire wall 14 that separates the engine compartment from the passenger compartment.
Vehicle instrument panels are generally located behind the steering wheel of a vehicle and include a number of gauges or other displays for providing a driver with information about vehicle conditions. In addition, air vents for distributing cooled and heated air throughout a passenger compartment are often mounted within an instrument panel. Instrument panels are conventionally mounted onto a vehicle firewall with the dash insulator disposed therebetween. FIG. 2 illustrates a conventional instrument panel 20. The illustrated instrument panel 20 includes an instrument cluster area 22, air vents 24, central console area 26 and glove box 28.
FIG. 3 illustrates a conventional automotive carpet assembly 30. The illustrated carpet assembly 30 has a nonplanar three dimensional molded configuration adapted to fit in the front seat compartment of an automobile and includes a raised medial portion 31 adapted to conform to the transmission hump, generally vertically extending side portions 32 adapted to fit beneath the door opening, and a front portion 33 adapted to fit along the inclined floorboard and portions of a vehicle firewall. Various openings or cut-outs are provided, as indicated at 34, to receive air conditioning equipment, the steering column, pedals and the like.
During vehicle manufacturing, dash insulators, instrument panels and floor coverings are typically installed separately. In addition, the installation of dash insulators, instrument panels and floor coverings can be complex and labor intensive. As such, vehicle manufacturers are continuously looking for ways to reduce costs and complexity associated with vehicle manufacturing.
U.S. Pat. No. 4,597,461 to Kochy et al. describes a pre-assembled module for the cockpit zone of a motor vehicle, which is adapted to be mounted as one single unit inside the vehicle body and which incorporates essentially the following components: an instrument board including all instruments and accessories commonly contained therein, fuse box and electric wiring, heater with controls and air distribution system; furthermore a steering system including steering wheel, steering column enclosure and steering support means; also pedals for clutch and brake, including mounting brackets. The vehicle body includes a fire wall and fire wall support member to which the aforementioned components and accessories are connected when in the installed position. The fire wall and fire wall support member are separated from the body shell and serve as an assembly base for the unit. In the installed position, the fire wall and fire wall support member are sealingly connected with the respective adjacent body panels.